1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and method for processing semiconductor substrates. More particularly, embodiments of the present invention relate to an electrostatic chuck used in a plasma chamber.
2. Description of the Related Art
Plasma enhance processes, such as plasma enhanced chemical vapor deposition (PECVD) process, high density plasma chemical vapor deposition (HDPCVD) process, plasma immersion ion implantation process (P3I), and plasma etch process, have become essential in semiconductor processing.
Plasma provides many advantages in manufacturing semiconductor devices. For example, using plasma enables a wide range of applications due to lowered processing temperature, plasma enhanced deposition has excellent gap-fill for high aspect ratio gaps and high deposition rates.
One problem that occurs during plasma processing is deformation of a substrate being processed, especially for a device substrate, i.e. a patterned substrate. Semiconductor devices are formed by stacking layers of materials by certain pattern on a semiconductor substrate. A patterned substrate may “bow” during processes due to differences in thermal expansion among layers of different materials, particularly when the substrate is being heated. Bowing of the substrate may lead to non uniformity of the process surface. Sides and back of a bowed substrate may be processed which not only wastes processing material, as precursors for plasma processing are usually very expensive, but also causes contaminations and other troubles for subsequent process steps.
FIG. 1 (prior art) schematically illustrates a substrate bowing scenario during a plasma process. A plasma reactor 10 comprises an electrode 12 connected to a radio frequency (RF) power 17 through an impedance matching circuit 16. A grounded electrode 11 is configured to support a substrate 13 thereon. The electrode 12 and the grounded electrode 11 form a capacitive plasma generator. When proper RF power is added to the electrode 12, a plasma 15 may be generated from any precursor gas supplied between the electrode 12 and the grounded electrode 11 to process the substrate 13. The substrate 13 may be heated by a heater 18 embedded in the grounded electrode 11. The plasma 15 also heats the substrate 13 during process. A plasma processing temperature may be between about 250° C. to about 450° C. The substrate 13 may bow as temperature rises. In some cases, the edge of a 300 mm substrate may bow as much as 0.4 mm. The bowing substrates are sometime referred as substrates with high curvatures.
Bowing of a substrate presents a challenge for process uniformity on a device side 14 of the substrate 13, which becomes more and more critical as feature size shrinks. External means, such as an electrostatic chuck or a vacuum chuck, are used to keep a substrate flat during processing. However, a chucked substrate may still become deformed during a plasma process due to heat dissipated by the plasma.
Therefore, there is a need for an apparatus and method for clamping a substrate while maintaining flatness of the substrate during a plasma process.